This invention relates to a technique for re-using wooden railroad ties and, in particular, for plugging the old spike holes after the old spikes have been removed.
To replace existing rails the spikes securing the rails through a tie plate to the ties have to be removed before the existing rails can be removed. The existing wooden ties are then usually inspected to determine which are still in a fit condition for re-use. Those which have deteriorated badly are replaced either with new ties or possibly with other old ties from a different site. Before the old ties can be re-used, it is necessary to plug the holes left by the old spikes so that, firstly, deterioration of the ties at the hole sites will be retarded, primarily by sealing against ingress of moisture, and so that new spikes can be driven into the ties to secure the new rails without the necessity for insuring that the spikes miss the old hole location; in other words, the plugged hole should be able to retain securely a new spike.
The conventional method of plugging spike holes in old wooden ties is by manually inserting wooden pegs which are then hammered into place. The process involves four men, two on each side of the track. On each side of the track one man inserts the pegs into the spike holes and the second drives the pegs into the holes with a ramrod.
Obviously, this technique is very labor intensive and is not compatible with automated or semi-automated track renewal systems which are being developed to replace and repair railroad track.
Other methods of plugging old spike holes have been proposed. For example, a sand mixture may be poured into the spike holes but this has several disadvantages. Firstly, the mixture is difficult to get into the hole, secondly it does not offer an effective seal against moisture and, thirdly it may not stay in the hole during service.
Another technique which has been proposed is the use of a plugging material which comprises a mixture of a granular abrasive material and a granular plastic material, these two components being thoroughly mixed to form a substantially homogeneous mixture which is poured into the holes. When a spike is driven into the hole containing the material, the friction between the spike and the abrasive material generates enough heat to plasticize the plastic material and, as a consequence, the plastic material flows and then cools to provide a bond between the spike and tie. Such a technique is disclosed in U.S. Pat. No. 4,070,201 which issued in Jan. 24, 1978 to Racine Railroad Products, Inc. as assignee.
A disadvantage of this last technique is that, unless the spike enters the filled hole, there will be no heat generated to cause flowing of the plastic material. Thus, in the case where a spike misses the hole, the material in the hole will remain in powder form and will not, therefore, serve to plug the hole effectively against the ingress of moisture.
A further disadvantage is that the plastic temperature of the material has to be controlled very carefully to ensure, on the one hand, that the material will not plasticize during storage in hot climates and that it will, on the other hand, plasticize in cold climates during the spike driving operation. In view of the fact that the heat generated during the spike driving operation is probably also a function of the type of spike driving equipment in use and the amount and type of abrasive in the mixture, it can be seen that it would be difficult to obtain a plugging mixture which is universal in the sense that it can operate under a full range of ambient temperatures.
Another disadvantage of the above technique is that it is probable that the spike holes have to be dry before the mixture can be applied or, at any rate, the technique may not be satisfactory during wet weather.
Finally, the cost of obtaining or preparing the mixture suitable for use in this technique is rather high.